FIELD OF THE INVENTION
The invention relates to a photosensitive, in particular photopolymerizable, material for the production of color proofing films for controlling color separations which are used to expose printing plates for multicolor printing. It furthermore relates to a color proofing method in which a multicolored image comprising a plurality of single-color images in register is produced on an image-receiving material. The single-color images are produced by laminating a film support coated with a photopolymerizable layer which has been dyed in a primary color onto the image-receiving material, exposing the layer with the corresponding color separation, and developing the image by peeling off the support with the non-image areas from the image receiving material. A multicolored image is produced by repeating the same steps with photopolymerizable layers in other primary colors.
A color proofing method of this general type and a material intended for this purpose are disclosed in U.S. Pat. Nos. 4,895,787 and 5,049,476. This material comprises a transparent film support, the surface of which has preferably been adhesion-pretreated, a photopolymerizable layer which contains a dye or a colored pigment in a primary color of multicolor printing, and a heat-activatable adhesive layer on the photopolymerizable layer. The material is laminated onto an image-receiving material, exposed through the film support and then developed by peeling off the film support from the image-receiving material, leaving the exposed areas of the colored photosensitive layer on the film support, and the unexposed areas together with the adhesive layer on the image-receiving material. The method thus works positively, i.e., a positive copy of the original is produced on the image-receiving material.
This processing method has the advantage of not requiring any alkaline or acidic solutions or organic solvents for development; disposal of these is therefore unnecessary. A disadvantage of this method is that the thermoplastic adhesive layers have a certain tendency toward blocking when the material is stacked or wound up. This can result in the adhesive layer sticking so strongly to the back of the adjacent film on extended storage, in particular at elevated temperature, that it cannot be separated therefrom without damage. Moreover, when these films are laid one on top of the other during lamination, air can be trapped, which cannot be removed again due to the tendency of the layers to block or stick, and then results in faults during processing.
U.S. Pat. No. 4,889,787 describes a photo-sensitive material for the production of color proofing films based on photosensitive diazo oxides. The material has an adhesive layer which contains silica particles. The particles described therein are said to reduce the tendency of the adhesive layer toward blocking and accordingly have a mean particle size in excess of the layer thickness. This material is developed by washing out the non-image areas to give the image.